As I read 1421, I was struck by how closely it resembled Jared Diamond's Guns, Germs, and Steel. They're both highly ambitious books that promise to turn history on its head, talk about plants and animals and the archaeological record, are full of world maps with arrows on them, and made it to The New York Times bestseller list. But the differences are just as revealing. Diamond is a darling of the literati and won the Pulitzer Prize for his book, while Menzies has racked up a long list of detractors. The original Times review for Guns, Germs, and Steel rather uncritically recounted its arguments, while the review for 1421 seriously questioned its many faults.

As much as this says about the vagaries of book reviews, it also suggests how to popularize history profitably. Make a splash, bring history to life, don't disappoint the reader, and you'll have a best-seller on your hands. The line between fact and fiction is increasingly blurred in the world of Da Vinci Code-style bestsellers.

Menzies, a retired Royal Navy submarine captain, claims that four separate Chinese fleets under the overall aegis of the great eunuch admiral Zheng He sailed on great voyages of discovery about the year 1421. During these voyages, they discovered the Americas, Antarctica, Oceania, various Pacific islands, and longitude — basically, every continent except Europe. The Zhu Di emperor's death, however, put an end to the great voyages of discovery. China turned her energies inwards, and records of the Zheng He voyages were destroyed. Within a century, though, Europeans picked up the mantle of discovery. These great explorers thus bravely set forth into the (not-quite) unknown, ultimately handing Europe the mantle of world dominance on the back of Chinese maps.

Startling though the claims may be, they are not new. Zheng He's voyages to Africa are well-known and taught in the standard histories, though he is generally considered to have stopped in Africa and never to have reached America. But it’s been a fixture of historical speculation for decades. After all, if Zheng He could precede European sailors to Africa, why could he not make it to America as well? Many on the fringes of history believed that he did. For example, Murray Leinster's 1934 time-travel story "Sidewise in Time" observes without the slightest doubt, "It just happens that the Chinese happened to colonize America first." (orig. Street and Smith Publications, reprinted in Before The Golden Age, ed. Isaac Asimov).

But Menzies is the boldest of the adherents, claiming to prove such speculation as fact. The evidence for this claim is helpfully summarized in an appendix in outline form. Menzies’ quest originated with examination of pre-Columbian European maps showing lands that they should not have been aware of, and through a series of maps he sees the line of transmission from Chinese sources. Why the Chinese? Because only they were advanced enough to have undertaken such a journey. What’s proof that it was the Chinese? Various artifacts left behind in the Americas, Africa, and Oceania, and the genealogical imprint of Chinese sailors and concubines left behind in the New World.

It's all very interesting, but hardly conclusive. Menzies traces the voyages chronologically, spreading the evidence out and mixing maps and artifacts with speculation on the routes they took, borne out by his experience as a submarine commander sailing the same seas. Yet he consistently uses terminology such as "the only logical evidence," "incontrovertible," "certain." Clearly his claims are not incontrovertible, considering how many academics have disputed his claims.

Academics tend to be very open to ideas with a sound foundation; history in particular gets turned upside down every once in a while. This casual disregard for any alternative viewpoints is what reminded me of Jared Diamond. I went to a book talk for Collapse, the successor to Guns, Germs, and Steel, and was shocked by how casually he dismissed any objections raised. "That's a good try, but it's completely wrong," he would say, then repeat something from his book that papered over the objection without addressing it. I'd rather an author admit that there could be alternative viewpoints — it suggests humility, a willingness to entertain other points of view, and most importantly, an awareness of the level of evidence necessary to overturn established history.

Also, constantly throughout the book, he refers to his website www.1421.tv, on which, he promises, more incontrovertible evidence will be put up. After reading the book, I went there expecting some voluminous material and some detailed rebuttals of his critics. But it turns out to be just more of the same. Even on the web site, citations are murky. "A professor" says this. Who? "More than 200 experts" in China were consulted, 85% of whom agree and 15% of whom disagree, and "details will be provided to any researcher who requests them." Why not just tell us? Even more questionable are some of the institutions listed as having been consulted on accuracy. The Overseas Chinese Affairs Office of the State Council of the People's Republic of China is doubtlessly filled with history experts, but would one rely on the US State Department to endorse a book on American history?

The postscript to the second edition of the book, which fixes some obvious errors that were criticized in the first edition but doesn't really address the more substantive and general, closes with: "The great bulk of the new evidence that has enabled me to make such startling claims has come from readers of my book. It is you, not historians or academics, who have rewritten history." As dashing as it may seem to be the lone voice of reason in a maddening crowd, ignoring the academic concepts of peer review and standards of proof is a very dangerous attitude to take. Secrecy is essential for some fields such as warfare and technology — generals must keep plans secret from the enemy, and inventors from their competitors. But on the battlefield of ideas, holding back your sources simply generates suspicion about your (un)willingness to engage in discussion.

As shaky as the thesis seems (the book would be better titled "1421: Did China Discover America?" with an all-important question mark), the book is nevertheless rather enjoyable as light reading. Historical detective work is filled with Eureka! moments, and many of Menzies' discoveries are fascinating and probably true (what’s problematic are the conclusions). When he looks at rare maps, or hunts down explanations for strange notation, it gives a vicarious thrill similar to that experienced in Alex Haley's Roots (or the final episode in the second miniseries)), as the author digs through archives to corroborate his oral family history. But while Roots concentrated the detective work in one section, making it easy to separate the plot from the process of discovery, 1421 intersperses them.

Chronological accounts do wonders for accounts of history, and Menzies is no exception. He was born in China during the period of Western domination, fondly recalls his Chinese amah, and has great respect for Chinese culture and history. His spectacular (and partly conjectural) description of the ceremonies surrounding the Forbidden City's opening bring to life the majesty, the pageantry, and the far-reaching influence of Imperial China at its peak. The reopening of the silted-up Grand Canal, the repair of the run-down Great Wall — all speak to the massive outlays of manpower and national effort that was made possible by the centralized administration that has characterized China for thousands of years.

His historical detective work and accounts of the Chinese fleet sailings are likewise absorbing. Here is where his credentials are strongest. His Navy background in astronavigation, currents, and wind are used to great effect. His theory of the Chinese discovery of longitude, explained in detail in an appendix, is a absorbing reconstruction of the technologies then available. That it was actually tested during a lunar eclipse make it all the more compelling. His reconstruction of coast lines before global warming has raised the sea to present-day levels is also thought-provoking.

As interesting as individual elements of his book may be, Menzies doesn't really prove that China discovered America. Before hearing of this book I gave no thought to the matter, leaving off at Zheng He's voyages to Africa. When I saw it on The Times' bestseller list, I thought, "Well, it's possible." After reading the book, I still think, "Well, it's possible." But that’s all it is. The book hasn’t really changed my opinion one way or another.